The present invention relates to an apparatus and method for remotely monitoring variables comprising of momentarily activated remote monitoring devices that are capable of transmitting data to a control device.
Remote sensors have been used for a number of years for monitoring and relaying information relating to the environment in which they are placed to a central monitoring system. The sensors are, for example, used to measure and record at regular intervals, environmental conditions such as temperature, humidity, gas concentration, geographic location and so on. Other examples are sensors that are used to measure mechanical quantities such as stress, strain, tilt, vibration and system integrity. Sensors can also be used to measure and record physiological variables such as heart rate, blood pressure, body temperature, and the like. Self-sensing electronic seals can also sense and record their own security state at regular intervals. For the purposes of this invention all types of these devices will be referred to as “remote monitoring devices.”
Prior art teaches that a control device can communicate with a plurality of monitors by “polling,” whereby only the correctly addressed monitor transmits or receives information. Unfortunately, this technique increases the power used by the monitors since each one must remain awake long enough to determine whether or not it is being addressed and each must also be awake at the right time to receive and check the next “poll.” For just one or two monitors this may not be serious problem, but if many thousands of electronic seals in a goods yard need to be polled on a regular basis, the lifetime of their batteries would be greatly reduced. In such situations, replacing drained batteries would be costly and impractical.
U.S. Pat. No. 6,100,806 discloses an apparatus and method for continuous electronic monitoring and tracking of individuals by utilising the Global Positioning System (GPS) satellites and cellular telephone communications. Remote units comprise the position and data sensor as well as a transmitter device to transmit the information back to a central tracking station. A problem associated with this system is the need for a constant supply of electricity in order to supply data continuously to the central tracking unit, thus the apparatus is only effective if remote batteries are replaced frequently. If the batteries are not replaced frequently, the apparatus quickly becomes inoperable and ineffective for tracking individuals or other data of interest.
U.S. Pat. No. 6,420,971 discloses a security seal whereby the seal awakes periodically, checks and records its security state, emits an infrared beacon, checks for a valid response from an remote device and returns to sleep if none is detected.